A vane pump includes a plurality of vanes housed in radial slits of a rotor. Each vane is biased in a direction to project from the slit by a hydraulic force of a vane back pressure chamber for pressing a base end part of the vane and a centrifugal force acting on the vane with the rotation of the rotor and a tip part of the vane slides in contact with an inner peripheral cam surface of a cam ring. The vanes sliding in contact with the inner peripheral cam surface reciprocate along the slits as the rotor rotates, whereby pump chambers expand and contract. Hydraulic oil pressurized in the pump chambers is discharged from discharge ports open on a side plate to a discharge pressure chamber in the vane pump and supplied from the discharge pressure chamber to a hydraulic device.
In such a vane pump, when the rotation of the rotor is stopped, the vanes located above the rotor fall toward the backs of the slits by gravity. Thus, there is a possibility that projecting movements of the vanes from the slits are delayed and a pump discharge pressure rises at a delayed timing at the start-up when the rotor is rotated again.
Accordingly, JP2004-360473A discloses a vane pump provided with a vane ring projecting in an axial direction of a rotor from a side plate. Since the vane ring holds base end parts of vanes when the rotation of the rotor is stopped, the vanes can be held in a state forcibly projected from slits.
The above vane pump includes a vane ring housing groove which is open on one end surface (side surface) of the rotor and in which the vane ring is housed, and a plurality of oil sump recesses which are open on the other end surface of the rotor and into which a pump discharge pressure is intermittently introduced. Since this causes pump-discharged oil to be supplied to the vane ring housing groove and each oil sump recess, an oil film is formed in a clearance between the rotor and the side plate to prevent seizure due to sliding contact.